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P0172 System Too Rich (Bank 1)
What it means
Bank 1 is getting too much fuel for the amount of air. The computer is pulling fuel out but can't correct enough.
Severity: Moderate
Can I drive it? Usually drivable short-term, but you'll burn extra fuel and can foul plugs and damage the catalytic converter.
Common causes (most likely first)
- Leaking fuel injector
- Faulty MAF sensor
- High fuel pressure / bad fuel pressure regulator
- Faulty upstream O2 sensor
- Faulty coolant temp sensor
- Restricted air filter
Likely fixes
- Replace dirty air filter
- Clean/test MAF sensor
- Test fuel pressure and regulator
- Check injectors and coolant temp sensor
DIY parts cost
$15–$300
Approximate estimate
Shop repair cost
$100–$900
Approximate estimate, parts + labor
DIY difficulty
Moderate
Varies by vehicle
Cost ranges are rough, approximate U.S. estimates and vary widely by vehicle, region, and parts brand. Always confirm the diagnosis before buying parts.
Parts you may need
- Engine air filterCheck price
- MAF sensor cleanerCheck price
- Fuel pressure regulatorCheck price
- Upstream oxygen sensorCheck price
- Coolant temperature sensorCheck price
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